This invention relates generally to filter and screen devices for use with underground fluid and gas extraction, sparging and monitoring equipment and more particularly, to a universal well screen filter for use with well sampling, monitoring, extraction and sparging equipment.
Numerous devices have been developed for extraction, monitoring, sparging, sampling and other related underground well operations. In particular, a number of these devices have been developed for groundwater sampling, extraction and monitoring and similar operations, such as those described in commonly owned U.S. Pat. Nos. 4,669,554; 5,046,568; 5,449,045; 5,570,747; and 5,669,454, each of which is incorporated herein by reference. These devices are commonly known as sampling devices and typically include a drive point at a lower end for penetrating the ground and a hollow tubular body for the passage of fluids to the ground surface.
More specifically, these sampling devices generally include a drive point having a lower portion specifically configured for ground penetration and an upper portion which is removably coupled to a tubular drive point holder or extension tube. An elongated annular drive rod or drive casing is coupled to an upper end of the tubular drive point holder to extend its length to the ground surface and to facilitate driving of the drive point into the ground. Typically, the drive rod consists of a number of hollow drive rod sections coupled together to form a drive rod string. An annular seal is seated between the tubular drive point holder and the removably coupled drive point to prevent the ingress of groundwater or soil during insertion of the sampling device into the ground.
An interior pipe or well casing extends coaxially through both the drive rod string and the drive point holder to couple with the drive point. This internal pipe includes a lower section at its bottom end which includes a series of perforations or other openings that allow the groundwater or other fluid to enter. The groundwater can then be extracted or otherwise accessed through the interior pipe for sampling, extracting or other operations. To prevent sanding in, silting in or other forms of clogging at the base of the well as well as filtering, the perforations at the lower section of the interior pipe are often finely spaced slits.
In a typical operation, a section of the elongated annular drive rod is coupled to the tubular point holder which is in turn removably coupled to a drive point. The upper end of the annular drive rod is pushed, driven or otherwise forced into the ground to form a borehole. Additional sections of annular drive rods may be sequentially connected together to form a pipe string and increase the depth of penetration. The sampling device eliminates the need for drilling, digging or other well operations as well as the associated need to remove or otherwise handle the displaced soil. These advantages are particularly useful when testing in contaminated soil.
Once the drive point reaches the desired location and depth, the annular drive rod, including the attached tubular point holder and any attached pipe string are withdrawn slightly. This slight retraction causes a portion of the sampling device and particularly, the tubular point holder, to slide upward with respect to the drive point which is frictionally restrained in the ground. This upward sliding motion opens a flow path between the drive point and the retracted tubular drive point holder and permits groundwater to enter the sampling device at the desired depth only. The groundwater is then accessed through the interior pipe to be tested, sampled or otherwise treated. The annular drive rod, including any attached drive rod string is then removed, leaving the drive point and interior pipe within the ground.
Because the annular space between the borehole and the interior pipe or well casing is typically quite small, pouring sand or other filter medium to provide filtration around the slotted interior pipe is difficult, time consuming and often impossible. Similarly, when the interior pipe is only provided at the lower portion of the borehole, using the drive rod as the fluid conduit, pouring sand from the surface would also be quite difficult if not impossible.
In an effort to overcome these problems and to enhance filtering, prepack well screens are commonly used. These devices replace the lower section of the interior pipe. Presently, prepack well screens use a slotted inner pipe which has a threaded end that threads directly to the remaining length of interior pipe or well casing. This is similar to the perforated interior pipe described above. However, the slotted inner pipe is housed within a larger diameter screen or mesh cylinder. The annular space between the outside of the interior screen and the interior of the outer screen is filled with a uniform sand which is large enough to be retained between the slotted inner pipe and surrounding outer screen. Caps are used to support the outer screen about the inner pipe and to retain the sand therebetween.
Currently, several manufacturers supply this general type of sampling device. Each manufacturer has their own style and configuration as well as providing differing sizes. These differing sampling devices, including those having different diameters, are used to create different diameter boreholes and to accommodate various quantities of groundwater as well as to allow usage with different diameter drive rods and interior pipes. As a result, each manufacturer produces their own interior pipe and accompanying well screen device. Thus, any user of a particular interior pipe or well casing must also carry a compatible prepack well screen.
These configurations of prepack well screens and techniques of operation have numerous disadvantages. In general, a users ability to purchase and supply interior pipes and prepack well screens is limited since both must now be matched for proper connection. This limits a purchaser""s ability to obtain components from various manufacturers. In addition, the need to always match the connecting ends leads to increased logistics and costs. There is thus, a need for a universal well screen filter which is capable of use with most any manufacturer""s interior pipe or well casing. There is also a need for such a universal well screen device which is simple to use and inexpensive to manufacture.
The present invention overcomes the aforementioned problems by providing a universal well screen filter jacket which is removably replaceable over the section of perforated interior pipe. This universal configuration provides a standardized screen filter which is useable for all applications using the specified interior pipe diameter regardless of the interior pipe""s manufacture, style or interconnection means. In addition, the present well screen filter utilizes a pair of spaced apart screen cylinders to form a dual walled filter sleeve or jacket. The use of dual screen walls provides a much greater filter surface area to facilitate the flow of filtration in addition to allowing the use of a finer filter medium aid reducing turbidity.
The present invention is generally directed to a well screen filter assembly for installation in a borehole formed in fluid bearing formations to filter fluid passing therethrough. The filter assembly includes a double cylinder screen filter which is removably replaceable over a perforated tubular fluid carrying member such as the lower section of an interior pipe. The screen filter filters the fluid which then passes into the tubular member through its perforations. The fluid may then be moved out of the hole through the tubular member.
The well screen filter includes an outer cylindrical meshed screen member and an inner cylindrical meshed screen member which is aligned concentrically with the first screen member. The inner screen member has a smaller diameter than the outer screen member and is positioned to define an annular filter space therebetween. The annular filter space is substantially filled with a filter medium which is designed to filter particulate materials from fluid passing through the medium while also reducing turbidity. An upper end cap is secured to an upper end of each of the spaced apart screen members to seal the annular space therebetween and a lower end cap is secured to a lower end of each of the spaced apart screen members to also seal the annular space therebetween. Both end caps are further adopted to snugly seal between the inner screen member and the tubular fluid carrying member. The well screen filter is configured for replaceable removal and positioning along the tubular member.
In another aspect of the present invention, the well screen filter assembly includes a dual screen wall filter which slidably fits over an interior tubular member such as a section of interior pipe. The interior pipe is adapted for passage of fluid and includes at least one perforation which allows fluid to pass through the surrounding screen filter and into the interior pipe. The screen filter is configured such that it is slidably removable and replaceable over the interior pipe and particularly, over the perforated portion of the lower section of the interior pipe. At least one fastener is used to secure the well screen filter to the interior pipe.
This invention, together with the additional features and advantages thereof, which was only summarized in the foregoing passages, will become more apparent to those of skill in the art upon reading the description of the preferred embodiments, which follows in the specification, taken together with the following drawings.